// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2016 Thomas Graf <tgraf@tgraf.ch>
 */

#include <linux/filter.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/types.h>
#include <linux/bpf.h>
#include <net/flow.h>
#include <net/lwtunnel.h>
#include <net/gre.h>
#include <net/ip.h>
#include <net/ip6_route.h>
#include <net/ipv6_stubs.h>

struct bpf_lwt_prog {
        struct bpf_prog *prog;
        char *name;
};

struct bpf_lwt {
        struct bpf_lwt_prog in;
        struct bpf_lwt_prog out;
        struct bpf_lwt_prog xmit;
        int family;
};

#define MAX_PROG_NAME 256

static inline struct bpf_lwt *bpf_lwt_lwtunnel(struct lwtunnel_state *lwt)
{
        return (struct bpf_lwt *)lwt->data;
}

#define NO_REDIRECT false
#define CAN_REDIRECT true

static int run_lwt_bpf(struct sk_buff *skb, struct bpf_lwt_prog *lwt,
                       struct dst_entry *dst, bool can_redirect)
{
        struct bpf_net_context __bpf_net_ctx, *bpf_net_ctx;
        int ret;

        /* Disabling BH is needed to protect per-CPU bpf_redirect_info between
         * BPF prog and skb_do_redirect().
         */
        local_bh_disable();
        bpf_net_ctx = bpf_net_ctx_set(&__bpf_net_ctx);
        bpf_compute_data_pointers(skb);
        ret = bpf_prog_run_save_cb(lwt->prog, skb);

        switch (ret) {
        case BPF_OK:
        case BPF_LWT_REROUTE:
                break;

        case BPF_REDIRECT:
                if (unlikely(!can_redirect)) {
                        pr_warn_once("Illegal redirect return code in prog %s\n",
                                     lwt->name ? : "<unknown>");
                        ret = BPF_OK;
                } else {
                        skb_reset_mac_header(skb);
                        skb_do_redirect(skb);
                        ret = BPF_REDIRECT;
                }
                break;

        case BPF_DROP:
                kfree_skb(skb);
                ret = -EPERM;
                break;

        default:
                pr_warn_once("bpf-lwt: Illegal return value %u, expect packet loss\n", ret);
                kfree_skb(skb);
                ret = -EINVAL;
                break;
        }

        bpf_net_ctx_clear(bpf_net_ctx);
        local_bh_enable();

        return ret;
}

static int bpf_lwt_input_reroute(struct sk_buff *skb)
{
        enum skb_drop_reason reason;
        int err = -EINVAL;

        if (skb->protocol == htons(ETH_P_IP)) {
                struct net_device *dev = skb_dst(skb)->dev;
                const struct iphdr *iph = ip_hdr(skb);

                dev_hold(dev);
                skb_dst_drop(skb);
                reason = ip_route_input_noref(skb, iph->daddr, iph->saddr,
                                              ip4h_dscp(iph), dev);
                err = reason ? -EINVAL : 0;
                dev_put(dev);
        } else if (skb->protocol == htons(ETH_P_IPV6)) {
                skb_dst_drop(skb);
                err = ipv6_stub->ipv6_route_input(skb);
        } else {
                err = -EAFNOSUPPORT;
        }

        if (err)
                goto err;
        return dst_input(skb);

err:
        kfree_skb(skb);
        return err;
}

static int bpf_input(struct sk_buff *skb)
{
        struct dst_entry *dst = skb_dst(skb);
        struct bpf_lwt *bpf;
        int ret;

        bpf = bpf_lwt_lwtunnel(dst->lwtstate);
        if (bpf->in.prog) {
                ret = run_lwt_bpf(skb, &bpf->in, dst, NO_REDIRECT);
                if (ret < 0)
                        return ret;
                if (ret == BPF_LWT_REROUTE)
                        return bpf_lwt_input_reroute(skb);
        }

        if (unlikely(!dst->lwtstate->orig_input)) {
                kfree_skb(skb);
                return -EINVAL;
        }

        return dst->lwtstate->orig_input(skb);
}

static int bpf_output(struct net *net, struct sock *sk, struct sk_buff *skb)
{
        struct dst_entry *dst = skb_dst(skb);
        struct bpf_lwt *bpf;
        int ret;

        bpf = bpf_lwt_lwtunnel(dst->lwtstate);
        if (bpf->out.prog) {
                ret = run_lwt_bpf(skb, &bpf->out, dst, NO_REDIRECT);
                if (ret < 0)
                        return ret;
        }

        if (unlikely(!dst->lwtstate->orig_output)) {
                pr_warn_once("orig_output not set on dst for prog %s\n",
                             bpf->out.name);
                kfree_skb(skb);
                return -EINVAL;
        }

        return dst->lwtstate->orig_output(net, sk, skb);
}

static int xmit_check_hhlen(struct sk_buff *skb, int hh_len)
{
        if (skb_headroom(skb) < hh_len) {
                int nhead = HH_DATA_ALIGN(hh_len - skb_headroom(skb));

                if (pskb_expand_head(skb, nhead, 0, GFP_ATOMIC))
                        return -ENOMEM;
        }

        return 0;
}

static int bpf_lwt_xmit_reroute(struct sk_buff *skb)
{
        struct net_device *l3mdev = l3mdev_master_dev_rcu(skb_dst(skb)->dev);
        int oif = l3mdev ? l3mdev->ifindex : 0;
        struct dst_entry *dst = NULL;
        int err = -EAFNOSUPPORT;
        struct sock *sk;
        struct net *net;
        bool ipv4;

        if (skb->protocol == htons(ETH_P_IP))
                ipv4 = true;
        else if (skb->protocol == htons(ETH_P_IPV6))
                ipv4 = false;
        else
                goto err;

        sk = sk_to_full_sk(skb->sk);
        if (sk) {
                if (sk->sk_bound_dev_if)
                        oif = sk->sk_bound_dev_if;
                net = sock_net(sk);
        } else {
                net = dev_net(skb_dst(skb)->dev);
        }

        if (ipv4) {
                struct iphdr *iph = ip_hdr(skb);
                struct flowi4 fl4 = {};
                struct rtable *rt;

                fl4.flowi4_oif = oif;
                fl4.flowi4_mark = skb->mark;
                fl4.flowi4_uid = sock_net_uid(net, sk);
                fl4.flowi4_dscp = ip4h_dscp(iph);
                fl4.flowi4_flags = FLOWI_FLAG_ANYSRC;
                fl4.flowi4_proto = iph->protocol;
                fl4.daddr = iph->daddr;
                fl4.saddr = iph->saddr;

                rt = ip_route_output_key(net, &fl4);
                if (IS_ERR(rt)) {
                        err = PTR_ERR(rt);
                        goto err;
                }
                dst = &rt->dst;
        } else {
                struct ipv6hdr *iph6 = ipv6_hdr(skb);
                struct flowi6 fl6 = {};

                fl6.flowi6_oif = oif;
                fl6.flowi6_mark = skb->mark;
                fl6.flowi6_uid = sock_net_uid(net, sk);
                fl6.flowlabel = ip6_flowinfo(iph6);
                fl6.flowi6_proto = iph6->nexthdr;
                fl6.daddr = iph6->daddr;
                fl6.saddr = iph6->saddr;

                dst = ipv6_stub->ipv6_dst_lookup_flow(net, skb->sk, &fl6, NULL);
                if (IS_ERR(dst)) {
                        err = PTR_ERR(dst);
                        goto err;
                }
        }
        if (unlikely(dst->error)) {
                err = dst->error;
                dst_release(dst);
                goto err;
        }

        /* Although skb header was reserved in bpf_lwt_push_ip_encap(), it
         * was done for the previous dst, so we are doing it here again, in
         * case the new dst needs much more space. The call below is a noop
         * if there is enough header space in skb.
         */
        err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
        if (unlikely(err))
                goto err;

        skb_dst_drop(skb);
        skb_dst_set(skb, dst);

        err = dst_output(dev_net(skb_dst(skb)->dev), skb->sk, skb);
        if (unlikely(err))
                return net_xmit_errno(err);

        /* ip[6]_finish_output2 understand LWTUNNEL_XMIT_DONE */
        return LWTUNNEL_XMIT_DONE;

err:
        kfree_skb(skb);
        return err;
}

static int bpf_xmit(struct sk_buff *skb)
{
        struct dst_entry *dst = skb_dst(skb);
        struct bpf_lwt *bpf;

        bpf = bpf_lwt_lwtunnel(dst->lwtstate);
        if (bpf->xmit.prog) {
                int hh_len = dst->dev->hard_header_len;
                __be16 proto = skb->protocol;
                int ret;

                ret = run_lwt_bpf(skb, &bpf->xmit, dst, CAN_REDIRECT);
                switch (ret) {
                case BPF_OK:
                        /* If the header changed, e.g. via bpf_lwt_push_encap,
                         * BPF_LWT_REROUTE below should have been used if the
                         * protocol was also changed.
                         */
                        if (skb->protocol != proto) {
                                kfree_skb(skb);
                                return -EINVAL;
                        }
                        /* If the header was expanded, headroom might be too
                         * small for L2 header to come, expand as needed.
                         */
                        ret = xmit_check_hhlen(skb, hh_len);
                        if (unlikely(ret))
                                return ret;

                        return LWTUNNEL_XMIT_CONTINUE;
                case BPF_REDIRECT:
                        return LWTUNNEL_XMIT_DONE;
                case BPF_LWT_REROUTE:
                        return bpf_lwt_xmit_reroute(skb);
                default:
                        return ret;
                }
        }

        return LWTUNNEL_XMIT_CONTINUE;
}

static void bpf_lwt_prog_destroy(struct bpf_lwt_prog *prog)
{
        if (prog->prog)
                bpf_prog_put(prog->prog);

        kfree(prog->name);
}

static void bpf_destroy_state(struct lwtunnel_state *lwt)
{
        struct bpf_lwt *bpf = bpf_lwt_lwtunnel(lwt);

        bpf_lwt_prog_destroy(&bpf->in);
        bpf_lwt_prog_destroy(&bpf->out);
        bpf_lwt_prog_destroy(&bpf->xmit);
}

static const struct nla_policy bpf_prog_policy[LWT_BPF_PROG_MAX + 1] = {
        [LWT_BPF_PROG_FD]   = { .type = NLA_U32, },
        [LWT_BPF_PROG_NAME] = { .type = NLA_NUL_STRING,
                                .len = MAX_PROG_NAME },
};

static int bpf_parse_prog(struct nlattr *attr, struct bpf_lwt_prog *prog,
                          enum bpf_prog_type type)
{
        struct nlattr *tb[LWT_BPF_PROG_MAX + 1];
        struct bpf_prog *p;
        int ret;
        u32 fd;

        ret = nla_parse_nested_deprecated(tb, LWT_BPF_PROG_MAX, attr,
                                          bpf_prog_policy, NULL);
        if (ret < 0)
                return ret;

        if (!tb[LWT_BPF_PROG_FD] || !tb[LWT_BPF_PROG_NAME])
                return -EINVAL;

        prog->name = nla_memdup(tb[LWT_BPF_PROG_NAME], GFP_ATOMIC);
        if (!prog->name)
                return -ENOMEM;

        fd = nla_get_u32(tb[LWT_BPF_PROG_FD]);
        p = bpf_prog_get_type(fd, type);
        if (IS_ERR(p))
                return PTR_ERR(p);

        prog->prog = p;

        return 0;
}

static const struct nla_policy bpf_nl_policy[LWT_BPF_MAX + 1] = {
        [LWT_BPF_IN]            = { .type = NLA_NESTED, },
        [LWT_BPF_OUT]           = { .type = NLA_NESTED, },
        [LWT_BPF_XMIT]          = { .type = NLA_NESTED, },
        [LWT_BPF_XMIT_HEADROOM] = { .type = NLA_U32 },
};

static int bpf_build_state(struct net *net, struct nlattr *nla,
                           unsigned int family, const void *cfg,
                           struct lwtunnel_state **ts,
                           struct netlink_ext_ack *extack)
{
        struct nlattr *tb[LWT_BPF_MAX + 1];
        struct lwtunnel_state *newts;
        struct bpf_lwt *bpf;
        int ret;

        if (family != AF_INET && family != AF_INET6)
                return -EAFNOSUPPORT;

        ret = nla_parse_nested_deprecated(tb, LWT_BPF_MAX, nla, bpf_nl_policy,
                                          extack);
        if (ret < 0)
                return ret;

        if (!tb[LWT_BPF_IN] && !tb[LWT_BPF_OUT] && !tb[LWT_BPF_XMIT])
                return -EINVAL;

        newts = lwtunnel_state_alloc(sizeof(*bpf));
        if (!newts)
                return -ENOMEM;

        newts->type = LWTUNNEL_ENCAP_BPF;
        bpf = bpf_lwt_lwtunnel(newts);

        if (tb[LWT_BPF_IN]) {
                newts->flags |= LWTUNNEL_STATE_INPUT_REDIRECT;
                ret = bpf_parse_prog(tb[LWT_BPF_IN], &bpf->in,
                                     BPF_PROG_TYPE_LWT_IN);
                if (ret  < 0)
                        goto errout;
        }

        if (tb[LWT_BPF_OUT]) {
                newts->flags |= LWTUNNEL_STATE_OUTPUT_REDIRECT;
                ret = bpf_parse_prog(tb[LWT_BPF_OUT], &bpf->out,
                                     BPF_PROG_TYPE_LWT_OUT);
                if (ret < 0)
                        goto errout;
        }

        if (tb[LWT_BPF_XMIT]) {
                newts->flags |= LWTUNNEL_STATE_XMIT_REDIRECT;
                ret = bpf_parse_prog(tb[LWT_BPF_XMIT], &bpf->xmit,
                                     BPF_PROG_TYPE_LWT_XMIT);
                if (ret < 0)
                        goto errout;
        }

        if (tb[LWT_BPF_XMIT_HEADROOM]) {
                u32 headroom = nla_get_u32(tb[LWT_BPF_XMIT_HEADROOM]);

                if (headroom > LWT_BPF_MAX_HEADROOM) {
                        ret = -ERANGE;
                        goto errout;
                }

                newts->headroom = headroom;
        }

        bpf->family = family;
        *ts = newts;

        return 0;

errout:
        bpf_destroy_state(newts);
        kfree(newts);
        return ret;
}

static int bpf_fill_lwt_prog(struct sk_buff *skb, int attr,
                             struct bpf_lwt_prog *prog)
{
        struct nlattr *nest;

        if (!prog->prog)
                return 0;

        nest = nla_nest_start_noflag(skb, attr);
        if (!nest)
                return -EMSGSIZE;

        if (prog->name &&
            nla_put_string(skb, LWT_BPF_PROG_NAME, prog->name))
                return -EMSGSIZE;

        return nla_nest_end(skb, nest);
}

static int bpf_fill_encap_info(struct sk_buff *skb, struct lwtunnel_state *lwt)
{
        struct bpf_lwt *bpf = bpf_lwt_lwtunnel(lwt);

        if (bpf_fill_lwt_prog(skb, LWT_BPF_IN, &bpf->in) < 0 ||
            bpf_fill_lwt_prog(skb, LWT_BPF_OUT, &bpf->out) < 0 ||
            bpf_fill_lwt_prog(skb, LWT_BPF_XMIT, &bpf->xmit) < 0)
                return -EMSGSIZE;

        return 0;
}

static int bpf_encap_nlsize(struct lwtunnel_state *lwtstate)
{
        int nest_len = nla_total_size(sizeof(struct nlattr)) +
                       nla_total_size(MAX_PROG_NAME) + /* LWT_BPF_PROG_NAME */
                       0;

        return nest_len + /* LWT_BPF_IN */
               nest_len + /* LWT_BPF_OUT */
               nest_len + /* LWT_BPF_XMIT */
               0;
}

static int bpf_lwt_prog_cmp(struct bpf_lwt_prog *a, struct bpf_lwt_prog *b)
{
        /* FIXME:
         * The LWT state is currently rebuilt for delete requests which
         * results in a new bpf_prog instance. Comparing names for now.
         */
        if (!a->name && !b->name)
                return 0;

        if (!a->name || !b->name)
                return 1;

        return strcmp(a->name, b->name);
}

static int bpf_encap_cmp(struct lwtunnel_state *a, struct lwtunnel_state *b)
{
        struct bpf_lwt *a_bpf = bpf_lwt_lwtunnel(a);
        struct bpf_lwt *b_bpf = bpf_lwt_lwtunnel(b);

        return bpf_lwt_prog_cmp(&a_bpf->in, &b_bpf->in) ||
               bpf_lwt_prog_cmp(&a_bpf->out, &b_bpf->out) ||
               bpf_lwt_prog_cmp(&a_bpf->xmit, &b_bpf->xmit);
}

static const struct lwtunnel_encap_ops bpf_encap_ops = {
        .build_state    = bpf_build_state,
        .destroy_state  = bpf_destroy_state,
        .input          = bpf_input,
        .output         = bpf_output,
        .xmit           = bpf_xmit,
        .fill_encap     = bpf_fill_encap_info,
        .get_encap_size = bpf_encap_nlsize,
        .cmp_encap      = bpf_encap_cmp,
        .owner          = THIS_MODULE,
};

static int handle_gso_type(struct sk_buff *skb, unsigned int gso_type,
                           int encap_len)
{
        struct skb_shared_info *shinfo = skb_shinfo(skb);

        gso_type |= SKB_GSO_DODGY;
        shinfo->gso_type |= gso_type;
        skb_decrease_gso_size(shinfo, encap_len);
        shinfo->gso_segs = 0;
        return 0;
}

static int handle_gso_encap(struct sk_buff *skb, bool ipv4, int encap_len)
{
        int next_hdr_offset;
        void *next_hdr;
        __u8 protocol;

        /* SCTP and UDP_L4 gso need more nuanced handling than what
         * handle_gso_type() does above: skb_decrease_gso_size() is not enough.
         * So at the moment only TCP GSO packets are let through.
         */
        if (!(skb_shinfo(skb)->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6)))
                return -ENOTSUPP;

        if (ipv4) {
                protocol = ip_hdr(skb)->protocol;
                next_hdr_offset = sizeof(struct iphdr);
                next_hdr = skb_network_header(skb) + next_hdr_offset;
        } else {
                protocol = ipv6_hdr(skb)->nexthdr;
                next_hdr_offset = sizeof(struct ipv6hdr);
                next_hdr = skb_network_header(skb) + next_hdr_offset;
        }

        switch (protocol) {
        case IPPROTO_GRE:
                next_hdr_offset += sizeof(struct gre_base_hdr);
                if (next_hdr_offset > encap_len)
                        return -EINVAL;

                if (((struct gre_base_hdr *)next_hdr)->flags & GRE_CSUM)
                        return handle_gso_type(skb, SKB_GSO_GRE_CSUM,
                                               encap_len);
                return handle_gso_type(skb, SKB_GSO_GRE, encap_len);

        case IPPROTO_UDP:
                next_hdr_offset += sizeof(struct udphdr);
                if (next_hdr_offset > encap_len)
                        return -EINVAL;

                if (((struct udphdr *)next_hdr)->check)
                        return handle_gso_type(skb, SKB_GSO_UDP_TUNNEL_CSUM,
                                               encap_len);
                return handle_gso_type(skb, SKB_GSO_UDP_TUNNEL, encap_len);

        case IPPROTO_IP:
        case IPPROTO_IPV6:
                if (ipv4)
                        return handle_gso_type(skb, SKB_GSO_IPXIP4, encap_len);
                else
                        return handle_gso_type(skb, SKB_GSO_IPXIP6, encap_len);

        default:
                return -EPROTONOSUPPORT;
        }
}

int bpf_lwt_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len, bool ingress)
{
        struct iphdr *iph;
        bool ipv4;
        int err;

        if (unlikely(len < sizeof(struct iphdr) || len > LWT_BPF_MAX_HEADROOM))
                return -EINVAL;

        /* validate protocol and length */
        iph = (struct iphdr *)hdr;
        if (iph->version == 4) {
                ipv4 = true;
                if (unlikely(len < iph->ihl * 4))
                        return -EINVAL;
        } else if (iph->version == 6) {
                ipv4 = false;
                if (unlikely(len < sizeof(struct ipv6hdr)))
                        return -EINVAL;
        } else {
                return -EINVAL;
        }

        if (ingress)
                err = skb_cow_head(skb, len + skb->mac_len);
        else
                err = skb_cow_head(skb,
                                   len + LL_RESERVED_SPACE(skb_dst(skb)->dev));
        if (unlikely(err))
                return err;

        /* push the encap headers and fix pointers */
        skb_reset_inner_headers(skb);
        skb_reset_inner_mac_header(skb);  /* mac header is not yet set */
        skb_set_inner_protocol(skb, skb->protocol);
        skb->encapsulation = 1;
        skb_push(skb, len);
        if (ingress)
                skb_postpush_rcsum(skb, iph, len);
        skb_reset_network_header(skb);
        memcpy(skb_network_header(skb), hdr, len);
        bpf_compute_data_pointers(skb);
        skb_clear_hash(skb);

        if (ipv4) {
                skb->protocol = htons(ETH_P_IP);
                iph = ip_hdr(skb);

                if (!iph->check)
                        iph->check = ip_fast_csum((unsigned char *)iph,
                                                  iph->ihl);
        } else {
                skb->protocol = htons(ETH_P_IPV6);
        }

        if (skb_is_gso(skb))
                return handle_gso_encap(skb, ipv4, len);

        return 0;
}

static int __init bpf_lwt_init(void)
{
        return lwtunnel_encap_add_ops(&bpf_encap_ops, LWTUNNEL_ENCAP_BPF);
}

subsys_initcall(bpf_lwt_init)